Summertime brings joy to most gardeners Ñ blooming flowers, fresh vegetables,
green grass. However, summer-feeding insects can wreak havoc on some of our
favorite plants. Bagworms (Thyridopteryx ephemeraeformis) are actively feeding
on evergreens in our area at this time. Bagworm larvae hatched at the end of
May, a little earlier than in most years. Bagworms are not restricted to the
host species on which they began feeding. A notable pest of evergreens such
as junipers, arborvitae, spruce, pine, and Eastern red cedar, they also feed
on deciduous trees and shrubs such as maples and crabapples. Evergreens may
sustain severe damage because leaf loss can cause branch death. Deciduous trees
and shrubs that have been infested generally produce a new flush of leaves and
survive. As the name implies, bagworm eggs and caterpillars/larvae live in bags
festooned with pieces of foliage from the plant. In the fall, winter, and spring,
the spindle-shaped bags hang from plants in the manner of Christmas ornaments.
Bagworms overwinter as eggs deposited in the bags (female pupal cases). Each
female produces 500 to 1,000 eggs in one bag. Generally larvae hatch from eggs
between late May and mid-June, depending on environmental conditions. Larvae
often drop from the bag on fine one- to three-foot silk strands. The strands,
caught by the wind, ÒballoonÓ the larvae to various locations on the host plant
or as far as hundreds of feet or even miles away. Each young bagworm floats
until its silk catches on an object or plant. The first mission of the new larva
is to form a bag. The larva remains in its bags as it feeds. This bag will increase
in size to accommodate the growing larva. By middle to late August, feeding
is complete and bagworms begin to pupate inside the bags. In roughly 7 to 10
days, bagworms change into adults and mate, after which the females lay eggs.
Young caterpillars, which are an eighth to a quarter of an inch long, initially
cause minimal damage, feeding only on the outer layer of leaves. Older larvae,
which measure three-quarters of an inch to one inch long, consume entire needles
or leaves. Caterpillars start feeding at the tops of a tree or shrub and progress
down the afflicted plant. Caterpillars are best controlled once they have settled
down and begun to feed. Feeding begins about two weeks after eggs hatch Ñ this
year, in late June. Raymond Cloyd, a University of Illinois entomologist, recommends
the use of insecticides Ñ among them Bacillus thuringiensis var. kurstaki (sold
as DiPel or Thuricide), cyfluthrin (Tempo), trichlorfon (Dylox), and spinosad
(Conserve) Ñ to control bagworms. Insecticide sprays are effective on the young
caterpillars. Older ones are difficult to control; and females feed less as
they prepare for reproduction. The bacterium B. thuringiensis is effective on
young caterpillars, but the material must be ingested, so thorough coverage
of all plant parts is essential. Spinosad works by way of contact and ingestion
and is quite effective in controlling bagworms. Cyfluthrin and trichlorfon are
recommended for larger caterpillars, but, again, thorough coverage is essential.
The best and most effective means of controlling bagworms is handpicking and
destroying bags from fall through midspring. With the use of this method, overwintering
eggs are removed before they hatch.
Jennifer Fishburn is the horticulture-unit educator for the
University of Illinois Sangamon-Menard Unit. Reach her at fishburn@uiuc.edu.
Butterfly-gardening program
Butterflies add beauty and surprise to any
garden, and with a little attention to detail, you can design butterfly-friendly
gardens. If you would like to learn how to attract these Òflowers of the air,Ó
plan to attend a presentation at 1 p.m. Tuesday, June 29, or 7 p.m. Thursday,
July 1, at the University of Illinois Extension Building at the Illinois State
Fairgrounds. Sandy Mason of the University of Illinois Extension Unit will describe
the kinds of garden plants that attract butterflies and share information about
the butterflies that are common to Illinois. Call 782-4617 to reserve a seat
and an information packet. The cost is $2.
This article appears in Jun 17-23, 2004.
